Study On Chromatographic Properties Of Dithienyl Benzothiadiazole And Cucurbit[n]urils As New Stationary Phases Of Capillary Gas Chromatography

For capillary gas chromatography(CGC), a selective stationary phase and an efficient column preparation method are the requisites for a GC column to achieve high-resolution separations. In this dissertation,dithienyl benzothiadiazole derivatives and cucurbit[n]urils(CBn) derivatives were utilized as new stationary phases for gas chromatographic separation, respectively. The novel aspects of this dissertation are summarized as follows:(1) The capillary columns coated with 4,7-di(thiophen-2-yl) benzothiadiazole(TBT) and 4,7-bis(5-dodecylthiophen-2-yl) benzothiadiazole(TBT-C12) for GC were prepared. This is the first example of using TBT derivatives as stationary phases for capillary GC separations. Both of the as-prepared columns were characterized as nonpolar nature by the determined McReynolds constants. The results showed that both TBT and TBT-C12 columns achieved excellent separations for n-alkanes, esters and polycyclic aromatic hydrocarbons(PAHs), and the TBT-C12 column exhibited better thermal stability(up to 280℃) than the TBT column. The present work also suggested that introduction of long alkyl chains onto the TBT structure favors the improvement of separation performance and thermal stability. Additionally, thermodynamic parameters suggested that the retention behavior of n-alkanes and PAHs on the TBT-C12 column was mainly controlled by entropy change. This work proves that TBT derivatives have a promising future as the new GC stationary phases.(2)Two novel TBT derivatives, 4,7-di(5-allyl-2-thienyl)-benzothiadiazole(TBT- R1) and 4-(5-allyl-2-thienyl)-7-(5-dodecyl-2-thienyl)-benzothiadiazole(TBT-R2) were coated on the inner wall of capillary columns as stationary phases for capillary GC separations. The results showed that the theoretical plate number of both TBT-R1 and TBT-R2 were more than 2000 plates/m, which increased significantly comparing with the previous TBT and TBT-C12 columns. The TBT-R1 and TBT-R2 columns had average polarity of 174 and 123 evaluated by McReynolds constants, respectively, suggesting their medium polar nature. Additionally, both of the as-prepared columns showed good separation performance for a variety of analytes such as n-alkanes, esters, aldehydes, ketones, alcohols, bromoalkanes, halogeno benzenes, BTEX and the Grob mixture, and exhibited nice peak shapes for analytes that are liable to peak-tailing in GC analysis. This may partially stem from the specific interactions between the analytes with aromatic heterocyclic and side chain groups of stationary phases, such as π-π interactions and H-bonding, owing to the unique molecular structure of TBT derivatives. The influence of different substituents to chromatographic selectivity was evaluated by GC separation of a variety of analytes bearing different polarities and different structure types. The results showed that some solutes revealed different elution order on the two columns, and TBT-R2 column, which contains two side chains with different polars, exhibited better selectivity than TBT-R1 column in the separations of a large range of both polar and nonpolar compounds. The results also indicated that the substituent groups of TBT derivatives containing different polarity and different molecular structures play an important role in the GC separations(3) The cucurbit[8]uril(CB8) and its coordination complex with cadmium(II)(CB8-Cd) were used to prepare capillary columns for GC. The stationary phases were characterized by column efficiency and McReynolds constants. Their separation performance was investigated by GC separations of mixtures of different types while a commercial column was used for comparison. The CB8 stationary phase achieved high resolution for a wide range of analytes from nonpolar to polar while the CB8-Cd stationary phase exhibited good separation mainly for nonpolar to weak polar analytes. After comparing the retention behavior, separation mechanism of using cucurbituril compounds as GC stationary phase was discussed. It was also worthwhile to note that the stationary phases CB8 and CB8-Cd were very suitable for separation of high-boiling point compounds such as PAHs comparable to or better than the reported GC stationary phases. Moreover, energy effect on the retention of analytes on CB8 and CB8-Cd stationary phases was examined by thermodynamic parameters, showing that retention on CB8 column was determined mainly by enthalpy change for polar analytes and by both enthalpy change and entropy change for weak polar analytes, whereas retention on CB8-Cd column was mainly controlled by entropy change. This work demonstrates the great potential of CBn stationary phases as new type of GC stationary phases in GC analysis.(4) The cucurbit[6]uril(CB6) and perhydroxycucurbit[6]uril(HOCB6) were used as stationary phases in CGC separation. The McReynolds’ constants indicated that the CB6 had weakly polar, which was similar to that of HP-5MS, in the range of non polar. The separations of the CB columns for a wide range of analytes with different polarities were further evaluated and compared with that on HP-5MS column. The results showed that the HOCB6 column exhibits higher separating capabilities for critical analytes with better peak shapes than CB6 and conventional columns, especially for some polar aromatic compounds. The advantageous separation feature of the HOCB6 column may originate from its unique structure and favorably balanced interactions with the analytes. This work demonstrated the excellent chromatographic performance of HOCB6 as a new GC stationary phase and its potential in separation science.